1. Field of the Invention
The present invention relates to active matrix display devices which control thin film luminescent devices, such as electroluminescent (EL) devices emitting light by a driving current flowing in an organic semiconductive film, and light-emitting diode (LED) devices using thin film transistors (hereinafter referred to as TFTs).
2. Description of Related Art
Active matrix display devices using current-control-type luminescent devices, such as EL devices or LED devices, have been proposed. The fact that luminescent devices used in such types of display devices have self-luminescent functions provides advantages, such as obviating installation of a backlight, whereas backlights are essential for liquid crystal display devices, and providing a wider viewing angle.
FIG. 22 is a block diagram of an active matrix display device using charge-injection-type organic EL devices. In the active matrix display device 1A shown in the drawing, a plurality of scanning lines gate, a plurality of data lines sig extending in a direction perpendicular to a direction of extension of the scanning lines gate, a plurality of common feed lines com extending along the data lines sig, and a plurality of pixels 7 in a matrix formed by the data lines sig and the scanning lines gate, are formed on a transparent substrate 10.
A data line driving circuit 3 and a scanning line driving circuit 4 are provided for the data lines sig and the scanning lines gate, respectively. Each pixel 7 is provided with a conduction control circuit 50 for supplying scanning signals from a scanning line gate, and a thin film luminescent device 40 emitting based on image signals supplied from a data line sig through the conduction control circuit 50.
In this example, the conduction control circuit 50 has a first TFT 20 for supplying scanning signals from the scanning line gate to a gate electrode; a holding capacitor cap for holding image signals supplied from the data line sig through the first TFT 20; and a second TFT 30 for supplying the image signals held in the holding capacitor cap to the gate electrode. The second TFT 30 and the thin film luminescent device 40 are connected in series between an opposite electrode op (described below) and a common feed line com. The thin film luminescent device 40 emits light by a driving current from the common feed line com when the second TFT 30 is in an ON mode, and this emitting mode is maintained by a holding capacitor cap for a predetermined time.
In such a configuration of an active matrix display device 1A, as shown in FIGS. 23, 24(A), and 24(B), the first TFT 20 and the second TFT 30 are formed of islands of a semiconductive film in each pixel 7. The first TFT 20 is provided with a gate electrode 21 as a part of a scanning line gate. In the first TFT 20, one source-drain region is electrically connected to a data line sig through a contact hole in a first insulating interlayer 51, and the other region is connected to a drain electrode 22. The drain electrode 22 extends towards the region of the second TFT 30, and this extension is electrically connected to a gate electrode 31 of the second TFT 30 through a contact hole in the first insulating interlayer 51. One source-drain region of the second TFT 30 is electrically connected to a relay electrode 35 through a contact hole of the first insulating interlayer 51, and the relay electrode 35 is electrically connected to a pixel electrode 41 of the thin film luminescent device 40 through a contact hole in a second insulating interlayer 52.
Each pixel electrode 41 is independently formed in each pixel 7, as shown in FIGS. 23, 24(B), and 24(C). An organic semiconductive film 43 and an opposite electrode op are formed above the pixel electrode 41 in that order. Although the organic semiconductive film 43 is formed in each pixel 7, a stripe film may be formed over a plurality of pixels 7. The opposite electrode op is formed not only in a display section 11 including pixels 7, but also over the entire surface of the transparent substrate 10.
With reference to FIGS. 23 and 24(A) again, the other source-drain region of the second TFT 30 is electrically connected to the common feed line com through a contact hole in the first insulating interlayer 51. An extension 39 of the common feed line com faces an extension 36 of the gate electrode 31 in the second TFT 30 separated by the first insulating interlayer 51 as a dielectric film to form a holding capacitor cap.
In the active matrix display device 1A, however, only the second insulating interlayer 52 is disposed between the opposite electrode op facing the pixel electrode 41 and the data line sig on the same transparent substrate 10, which is unlike liquid crystal active matrix display devices; hence, a large capacitance is formed in the data line sig, and the data line driving circuit 3 is heavily loaded.
Accordingly, as shown in FIGS. 22, 23, 25(A), 25(B), and 25(C), the present inventors propose a reduction in parasitic capacitance in the data line sig by providing a thick insulating film (a bank layer bank; the region shaded with lines slanting downward to the left at a wide pitch) between the opposite electrode op and the data line sig. Furthermore, the present inventors propose that the region for forming the organic semiconductive film 43 be surrounded with the insulating film (bank layer bank) to block a solution discharged from an ink-jet head and to prevent bleeding of the solution towards sides in the formation of the organic semiconductive film 43.
When the entire bank layer bank is formed of a thick inorganic material in adoption of such a configuration, a problem of a prolonged film forming time arises. When the thick inorganic film is patterned, the pixel electrode 41 may be damaged due to overetching. On the other hand, when the bank layer bank is formed of an organic material, such as a resist, the organic semiconductive film 43 may deteriorate at the boundary between the organic semiconductive film 43 and the bank layer bank by the effects of the solvent components contained in the organic material in the bank layer bank.
Since formation of a thick bank layer bank causes formation of a large step difference bb, the opposite electrode op formed above the bank layer bank readily breaks on the step difference bb. Such breakage of the opposite electrode op due to the step difference bb causes insulation of the opposite electrode op from the neighboring opposite electrodes op to form point or linear defects in the display. When the opposite electrode op breaks along the outer periphery of the bank layer bank which covers the surfaces of the data line driving circuit 3 and the scanning line driving circuit 4, the opposite electrode op in the display section 11 is completely insulated from a terminal 12 and thus no image is displayed.
Accordingly, it is an object of the present invention in view of the above problems to provide an active matrix display device, without damage of thin film luminescent devices, having a thick insulating film satisfactorily formed around an organic semiconductive film in the thin film luminescent devices.
It is another object of the present invention to provide an active matrix display device without breakage of an opposite electrode formed on a thick insulating film which is formed around an organic semiconductive film to reduce parasitic capacitance.
The present invention for solving the above-mentioned problems is characterized by an active matrix display device comprising a display region including a plurality of scanning lines on a substrate, a plurality of data lines extending in a direction perpendicular to a direction of extension of the scanning lines, and a plurality of pixels arranged in a matrix bounded by the data lines and the scanning lines; each of the pixels being provided with a thin film luminescent device having a conduction control circuit containing a thin film transistor that supplies a scanning signal to a gate electrode through one of the scanning lines, a pixel electrode, an organic semiconductive film deposited above the pixel electrode, and an opposite electrode deposited above the organic semiconductive film; the thin film luminescent device emitting light based on an image signal supplied from the data line through the conduction control circuit; wherein the region that forms the organic semiconductive film is divided by an insulating film which is thicker than the organic semiconductive film; and the insulating film comprises a lower insulating layer which is formed of an inorganic material and is thicker than the organic semiconductive film, and an upper insulating layer which is deposited on the lower insulating layer and is formed of an organic material.
In the present invention, the data line will form large parasitic capacitance if the opposite electrode is formed on the entire surface of the display section to face the data line; however, a thick insulating film is provided between the data line and the opposite electrode in the present invention to prevent formation of the parasitic capacitance in the data line. As a result, a load on the data line driving circuit is reduced, and low energy consumption and high-speed display operation are achieved. If the thick insulating film is formed of only an inorganic material, a long film deposition time is required, resulting in low productivity. In the present invention, only the lower insulating layer in contact with the organic semiconductive film of the thin film luminescent device is formed of an inorganic material, and an upper insulating layer that includes an organic material, such as a resist, is formed thereon. Improved productivity is provided, since the upper insulating layer formed of an organic material facilitates formation of a thick film. The upper insulating layer does not come into contact with the organic semiconductive film, but the lower insulating layer formed of an inorganic material does come into contact with the organic semiconductive film; hence, the organic semiconductive film is protected from deterioration affected by the upper insulating layer. Accordingly, the thin film luminescent device does not cause decreased luminescent efficiency or reliability.
It is preferable in the present invention that the upper insulating layer be deposited in an inner region of the lower insulating layer so as to have a width narrower than that of the upper insulating layer. Such a two-step configuration prevents contact of the upper insulating layer formed of an organic material with the organic semiconductive film; hence deterioration of the organic semiconductive film can be more securely prevented. In such a two-step configuration, both the lower insulating layer and the upper insulating layer may be formed of inorganic materials.
Another aspect of the present invention is an active matrix display device comprising a display region including a plurality of scanning lines on a substrate, a plurality of data lines extending in a direction perpendicular to a direction of extension of the scanning lines, and a plurality of pixels arranged in a matrix bounded by the data lines and the scanning lines; each of the pixels being provided with a thin film luminescent device having a conduction control circuit containing a thin film transistor that supplies a scanning signal to a gate electrode through one of the scanning lines, a pixel electrode, an organic semiconductive film deposited above the pixel electrode, and an opposite electrode deposited above the organic semiconductive film; the thin film luminescent device emitting light based on an image signal supplied from the data line through the conduction control circuit; wherein the region that forms the organic semiconductive film is divided by an insulating film which is thicker than the organic semiconductive film; and the insulating film comprises a lower insulating layer formed of an inorganic material, and an upper insulating layer, formed of an inorganic material, so as to have a width which is narrower than that of the lower insulating layer.
In such a configuration, after films formed of inorganic materials, constituting a lower insulating layer and an upper insulating layer, are formed, the upper insulating layer is patterned. Since the lower insulating layer functions as an etching stopper, the pixel electrodes will not be damaged by slight overetching. After the patterning, the lower insulating layer is patterned. Since only one layer of the lower insulating layer is etched, the etching is readily controlled so that overetching, which would damage the pixel electrodes, does not occur.
It is preferable in the present invention that the conduction control circuit be provided with a first TFT that supplies the scanning signal to the gate electrode, and a second TFT of which the gate electrode is connected to the data line through the first TFT, and that the second TFT and the thin film luminescent device be connected in series between a common feed line formed in addition to the data line and the scanning line supplying a drive current and the opposite electrode. Although the conduction control circuit can be formed of a TFT and a holding capacitor, the conduction control circuit of each pixel is preferably formed of two TFTs and two holding capacitors to improve display quality.
It is preferable in the present invention that the insulating film be used as a bank layer which prevents bleeding of a discharged solution when the organic semiconductive film is formed by an ink-jet process in a region delimited by the insulating film. The insulating film preferably has a thickness of 1 xcexcm or more.
It is preferable in the present invention that a region, overlapping the area that forms the conduction control circuit in the region that forms the pixel electrode, be covered with the insulating film. That is, it is preferable that among the region that forms the pixel electrode, the thick insulating film be opened only at the flat section not having the conduction control circuit and the organic semiconductive film be formed only at the interior thereof. Such a configuration can prevent display irregularities due to an irregular thickness of the organic semiconductive film.
A thinner section of the organic semiconductive film causes a concentration of the driving current of the thin film luminescent device and decreased reliability; however, this configuration can prevent such a problem. If the organic semiconductive film emits light due to a driving current between a pixel electrode and the opposite electrode in the region overlapping the conduction control circuit, the light is shielded by the conduction control circuit and does not contribute to display. The driving current not contributing to display by the shielding effect of the conduction control circuit is an unavailable current.
In the present invention, the thick insulating film is formed at the section, in which such an unavailable current is expected, to prevent formation of the unavailable current. As a result, a current in the common feed line can be reduced. Thus, by reducing the width of the common feed line, a luminescent area can be increased, improving display characteristics, such as luminance and contrast.
In the present invention, the corners bounded by the insulating film may be rounded so that the organic semiconductive film has a rounded planar shape. The organic semiconductive film having such a shape avoids the concentration of the driving current at the corners, hence defects, such as insufficient voltage resistance, can be prevented at the corners.
When the organic semiconductive film having a striped pattern is formed, the lower insulating layer of the insulating film is formed so as to cover the area for forming the conduction control circuit in the region that forms the pixel electrode, the data line, the common feed line, and the scanning line, whereas the upper insulating layer is formed so as to form a striped pattern along the data line, and the organic semiconductive film is formed in the region bounded by the striped pattern of the upper insulating layer by, for example, an ink-jet process.
In such a configuration, the conduction control circuit is covered with the lower insulating layer so that only the organic semiconductive film formed at the flat section of the pixel electrode contributes to luminescence. That is, the thin film luminescent device is formed only at the flat section of the pixel electrode. Thus, the resulting organic semiconductive film has a constant thickness and does not display irregularities. Since the lower insulating layer prevents a driving current in the section not contributing to display, an unavailable current in the common feed line can be prevented.
In such a configuration, the section in which the lower insulating layer overlaps the upper insulating layer can be used as a bank layer to prevent bleeding of a discharged solution when the organic semiconductive film is formed by an ink-jet process. When the insulating film is used as a bank layer, the overlapping section of the lower insulating layer and the upper insulating layer preferably has a thickness of 1 xcexcm or more.
It is preferable in the present invention that the insulating film have a first discontinuities portion so that opposite electrodes of adjacent pixels are connected to each other at flat sections formed by the first discontinuities portion. The thick insulating film in the present invention may form a large step which causes breakage of the opposite electrode formed thereon; however, the first discontinuities portion formed at predetermined positions of the thick insulating film are planarized. Since the opposite electrodes of individual regions are electrically connected to each other at the flat sections corresponding to the first discontinuities portion, the opposite electrodes are protected from breakage even if breakage occurs at the step due to the insulating film. Since breakage of the opposite electrode formed above the insulating film does not occur when a thick insulating film is formed around the organic semiconductive film to suppress the parasitic capacitance, display quality and reliability of the active matrix display device can be improved.
When the insulating film is formed along the data line and the scanning line so as to surround the region that forms the organic semiconductive film, the first discontinuities portion are preferably formed between the adjacent pixels in the direction of the extending data line, between the adjacent pixels in the direction of the extending scanning line, or between the adjacent pixels in these directions.
When the insulating film extends in a striped pattern along the data line, the first discontinuity may be formed on at least one end of the extending direction.
It is preferable in the present invention that the periphery of the display section be provided with a data line driving circuit that supplies data signals through the data lines, and a scanning line driving circuit that supplies scanning signals through the scanning lines, that the insulating film be also formed above the scanning line driving circuit and the data line driving circuit, and that the insulating film have a second discontinuity at a position between the region that forms the scanning line driving circuit and the region for forming the data line driving circuit so that the opposite electrodes at the display section and at the peripheral section of the substrate are connected through the flat section. Even if breakage of the opposite electrodes occurs along the periphery of the insulating film which covers the data line driving circuit and the scanning line driving circuit, the opposite electrode at the display section is connected to the opposite electrode at the periphery of the substrate via the flat section, and thus electrical connection between these opposite electrode can be ensured.
In the discontinuity of the present invention, both the lower insulating layer and the upper insulating layer may have the discontinuity, or only the upper insulating layer among the upper insulating layer and the lower insulating layer may have the discontinuity.